Vascular disease in man has become one of the primary causes of poor overall health and death in recent years. Vascular diseases occur throughout the body and affect the heart, limbs and other parts of the body. Arterial disease has caused death by heart attack, reduced physical activity due to constriction or blockage of vessels or arteries serving the muscles of the heart, and constriction or blockage of vessels and arteries to the limbs, particular to the legs. These vascular diseases have resulted in the loss of extremities when the blood flow becomes sufficiently restricted to prevent proper nourishment of the tissue of the extremities and have caused death when reduced blood flow to the muscles of the heart have starved the heart of needed blood.
Each year, hundreds of thousands of revascularization procedures for angina are performed in the world. Mild cardial revascularization and limb salvation which are well accepted procedures for treatment of arterial diseases depend upon a readily available supply of prostheses or vascular transplants for the purposes of returning proper levels of blood flow to affected parts of the body. The availability of a suitable vascular prosthesis or transplant is frequently a limiting factor in decisions to treat such diseases through surgical procedures, including coronary artery bypass surgery.
A variety of techniques and prostheses have been tried in an effort to provide a surgically applied prosthesis capable of restoring proper blood flow to the afflicted part of the body. Modern synthetic fabric technology has provided one form of prosthesis which has been tried as a substitute for diseased arteries and vessels. Such synthetic fabrics are woven into tubes of fabric which may be sutured to the ends of blood vessels in order to provide a bypass or a replacement for a diseased section of the vessel. Such prostheses present a number of problems for surgeons and for patients. Successful grafting of such fabric replacement prostheses requires an extended convalescence during which collagenous tissue generated by the body must become implanted in the fabric prosthesis in order to ensure a successful long-term graft. This lengthy convalescence exposes the patient to an extended period of time during which hemorrhage may occur in the prosthesis and at the site of the connection. Failure requires additional emergency surgical procedures. Further, there is always the danger that unfavorable reaction to the implanted fabric material will occur and prevent the long-term use of the fabric prosthesis in the patient.
Another procedure frequently adopted for the replacement of restricted and affected vascular sections involves the harvesting of venus grafts from other parts of the body. Commonly, sections of vessel are removed from the patient's legs and implanted in the coronary artery system. Surgical removal of vessels from the leg complicates the surgical treatment of coronary bypass procedures because the surgeon must in effect perform two surgical procedures. One procedure involves opening the chest cavity and the other involves harvesting the sections of vessel from the legs. This naturally increases the operative time associated wit vessel procurement with an increased danger to the patient Even successful bypass surgery of this type presents the patient with added distress during the recuperation period since healing must take place not only at the site of the surgical graft implant but also at the site of the harvesting of the vessel section.
A readily available supply of vascular grafts is desirable since emergency repair or grafting of arterial or venous sections must frequently be undertaken on relatively short notice. For this reason, one attempt to provide a readily available supply of such surgical grafts is outlined in U.S. Pat. No. 4,319,363 in which a vascular prosthesis and methods of making such a prosthesis are outlined. In this particular patent, the vascular prosthesis is generated in a non-human host. A tube of collagenous material reinforced by a fiber mesh is obtained through implantation in a non-human host and removed from the host after a predetermined growth of collagenous tissue has become implanted in the fiber mesh. After removal of the tube of fiber-impregnated collagenous tissue, the tissue is tanned in order to provide a source of a vascular prosthesis suitable for surgical grafting in human patients. An obvious disadvantage of such a vascular prosthesis involves a non-human host and therefore potential tissue incompatibility by a human patient. The patient on which such a graft is used may reject the foreign tissue since the non-human tissue is clearly a foreign body of a type commonly rejected by the human body.
In order to avoid tissue rejection, the best tissue available for vascular grafting is the patient's own body tissue. As indicated previously, one approach to using the patient's own tissue is to harvest vessel sections from the leg. Frequently, immediate replacement of constricted and diseased sections of arteries and vessels is not necessary. If sufficient time is available to the patient, tissue can be grown in the patient's own body in order to generate a tube of collagenous tissue which may be used as a graft. Charles Howard Sparks provided a method and apparatus for generating such tubes of collagenous material and these methods and devices are described in U.S. Pat. Nos. 3,866,609, 3,707,958 and 3,866,247. In these patents, Sparks describes a method and apparatus for generating tubes of collagenous material by forming a tunnel in muscle tissue located in or adjacent to the groin area of the body. A mandrel bearing a coat of fibrous material is inserted into the tunnel in the muscle tissue and surgically implanted in the muscle tissue for a period of time sufficient for the body to generate a growth of collagenous material which impregnates the fibrous material. The mandrel implant is then surgically removed from the surrounding muscle tissue for use as a vascular graft in the patient.
This method and the collagenous section of tube produced by this growth of collagenous tissue presents several disadvantages. First, the patient is required to undergo a rather extensive surgical procedure in the removal of the collagenous implant. The collagenous tube is generated as a tube which is thoroughly connected to and become a part of the surrounding muscle tissue. The collagenous tube must be very carefully removed from the surrounding muscle tissue before it may be used as a vascular graft. Further, the collagenous tissue generated by this procedure is muscle tissue and therefore a type of collagenous tissue which is characteristic of muscle tissue. It is not characteristic of the tissue normally associated with artery and vessel walls.
Medical investigation has revealed that there are noticeable differences between collagenous tissue generated in muscle tissue and collagenous tissue which is generated in or near the vascular system. While the collagenous tissue generated in the muscle tissue of a patient will be compatible with the patient's body tissues, it nevertheless is not of the same type of tissue normally associated with the vascular system and accordingly is not as desirable as a vascular graft as might be desirable.
Additionally, collagenous tubes formed in the muscle tissue may be nicked by the surgeon's instruments when removed and generally has walls of varying thickness. These walls of varying thickness can cause complications in the patient's circulatory system when such tissue is used as grafts.
Harvesting venous sections from other parts of the body also is less than satisfactory because the harvested sections are frequently of larger than optimum diameter. Small diameter transplants of good quality are difficult to obtain. Use of large diameter transplants results in difficult surgical procedures to connect the transplant because of this incompatability of size.
Thus it is apparent that past methods and apparatus for supplying vascular grafts have not been entirely successful. Such prior procedures and grafts have encountered problems with tissue rejection, extended convalescence, extended exposure to infection, lengthy surgical procedures and other risks attendant to coronary arterial bypass surgery and similar vascular graft surgery.